System and method for assessment of retinal and choroidal blood flow noninvasively using color amplification

ABSTRACT

A system and method for assessing blood flow include: an ocular lens; a light source; a digital video camera; a biosensor; a trigger; and a computer. The ocular lens is for viewing a fundus of an eye. The light source is for illuminating the fundus. The digital video camera is for imaging the fundus. The biosensor is for sensing a pulse waveform. The computer is configured for: recording input frames and pulse waveform data in response to an input from the trigger; defining a low-pass frequency and a high-pass frequency from the pulse waveform data; stabilizing the input frames; enhancing contrast of the input frames; separating the input frames into sub-channels; conducting eulerian video magnification for color amplification using the inputs of image sampling rate, the low-pass frequency, the high-pass frequency, and an amplification factor; reconstructing the sub-channels into output frames; and combining the output frames with the input frames.

RELATED APPLICATIONS

This application claims priority to U.S. Provisional Patent ApplicationNo. 62/593,045, filed Nov. 30, 2017, the entire disclosure of which isincorporated herein by reference.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

The presently disclosed subject matter was made with support from theU.S. Government under Grant Number TL1TR001997 awarded by the NationalInstitutes of Health. Thus, the U.S. Government has certain rights inthe presently disclosed subject matter.

BACKGROUND OF THE INVENTION 1. Field of the Invention

The presently-disclosed subject matter relates to a system and methodfor assessment of retinal and choroidal blood flow noninvasively usingcolor amplification.

2. Description of Related Art

Diabetic Retinopathy (DR) is an increasingly prevalent disease and aleading contributor of all-cause blindness worldwide. Approximatelyone-third of the nearly 285 million diabetes mellitus patients worldwidehave signs of DR. In addition to retinal changes, choroidalabnormalities are common in patients with diabetes. The choroid—thevascular layer of the eye between the retina and the sclera—suppliesblood to the outer layers of the retina including the retinal pigmentedepithelium (RPE) and photoreceptors. Despite growing evidence ofchoroidal abnormalities present in diabetes, it remains unclear howthese changes clinically impact diabetic patients. Decreased choroidalblood flow is thought to be the primary event leading to diabeticretinopathy. Therefore, it is critical to understand vasculardevelopment of and events leading to abnormalities of choroid vessels.Although the retina itself is readily available for imaging, the RPEobscures the choroid, making it difficult to visualize using standardophthalmic imaging techniques. This difficulty hinders efforts in usingchoroidal abnormalities as a predictive factor of disease evolution andresponse. Indocyanine green (ICG) angiography, which utilizes a dye thatcan be seen through the RPE layer, has been used clinically to visualizechoroidal vessel filling abnormalities in the eyes of patients withretinopathy. Although this technique can detect gross vascular defects,it does not provide much information concerning anatomic or structuralfeatures of the choroid, and it requires static images takensequentially over minutes. Additionally, the ICG contrast dye is knownto cause allergic reactions and requires venipuncture making thetechnique invasive to the patient. The National Eye Institute hasidentified the need to engineer and apply new methods and imageprocessing techniques to study blood flow in the retina and choroid,with the ultimate goal of translating these imaging technologies intocost-effective and easy-to-use platforms for routine clinical use.

BRIEF SUMMARY OF THE INVENTION

In accordance with one aspect of the invention, a system for assessingretinal and choroidal blood flow in a subject, includes: an ocular lens;a light source; a digital video camera; a biosensor; a trigger; acomputer; and a display. The ocular lens is for viewing a fundus of aneye of the subject. The light source is for illuminating the fundus ofthe eye of the subject. The digital video camera is in opticalcommunication with the ocular lens for imaging the fundus of the eye ofthe subject. The biosensor is for sensing a pulse waveform of thesubject. The computer is in communication with the digital video camera,the biosensor, and the trigger. The computer is configured for:recording input frames received from the digital video camera and pulsewaveform data from the biosensor in response to an input from thetrigger; defining a low-pass frequency and a high-pass frequency by alowest time and a highest time between heart beats in the pulse waveformdata; stabilizing each of the input frames utilizing subpixel phasecorrelation with a reference frame; enhancing contrast of each of theinput frames utilizing contrast limited adaptive histogram equalization(CLAHE); separating each of the input frames into sub-channels;conducting on each sub-channel eulerian video magnification for coloramplification using the inputs of image sampling rate, the low-passfrequency, the high-pass frequency, and an amplification factor;reconstructing the amplified sub-channels into output frames; andcombining the output frames with the input frames, resulting in enhancedframes demonstrating retinal and choroidal blood flow and tissueperfusion. The display is for displaying the enhanced frames.

In one implementation, the system further includes a head and chin restfor the subject to rest comfortably without strain.

In another implementation, the system includes a fixation illuminatorattached to the ocular lens to reduce ocular movements.

In yet another implementation, the biosensor is a pulse oximeter.

In another embodiment, the computer is further configured for adjustingthe enhanced frames for brightness, contrast, zoom, or rotation.

In yet another embodiment, the computer is further configured forquantifying image intensity for a user-selected region of interest (ROI)and generating a heat map of the ROI where intensity changes aregreatest.

The amplification factor may be a scalar, or may be function-based.

In accordance with another aspect of the invention, a method forassessing retinal and choroidal blood flow in a subject, includes:recording, by a computer in response to an input from a trigger, inputframes received from a digital video camera and an ocular lensconfigured for imaging a fundus of an eye of the subject; recording, bythe computer in response to the input from the trigger, pulse waveformdata of the subject received from a biosensor; defining a low-passfrequency and a high-pass frequency by a lowest time and a highest timebetween heart beats in the pulse waveform data; stabilizing each of theinput frames utilizing subpixel phase correlation with a referenceframe; enhancing contrast of each of the input frames utilizing contrastlimited adaptive histogram equalization (CLAHE); separating each of theinput frames into sub-channels; conducting, on each sub-channel,eulerian video magnification for color amplification using the inputs ofimage sampling rate, the low-pass frequency, the high-pass frequency,and an amplification factor; reconstructing the amplified sub-channelsinto output frames; and combining the output frames with the inputframes, resulting in enhanced frames demonstrating tissue perfusion.

In one implementation, the method further includes illuminating the eyeof the subject with a fixation illuminator to reduce ocular movements.

In another implementation, the method further includes saving theenhanced frames sequentially to a video file. Alternatively, the methodmay further include displaying the enhanced frames live on a display.

In yet another implementation, the method further includes waiting tountil enough pulse waveform data has been recorded to define thelow-pass frequency and the high-pass frequency before stabilizing eachand enhancing the contrast of each of the input frames.

In one embodiment, the pulse waveform data is a pulse oximeter signal,and the method further includes cross-correlating the pulse oximetersignal with the input frames, including: performing temporal fastfourier transform of the input frames; performing temporal fast fouriertransform of the pulse oximeter signal; determining a matrix product bymatrix multiplication of the temporal fast fourier transform of theimage frames with a complex conjugate of the temporal fast fouriertransform of the pulse oximeter signal; performing inverse fast fouriertransform of the matrix product; determining a peak of the inverse fastfourier transform of the matrix product to obtain a time delay betweenthe pulse oximeter signal land the image frames; and shifting the pulseoximeter signal by the time delay.

The amplification factor may be a scalar, or may be function-based.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of an exemplary system for assessingretinal and choroidal blood flow in a subject, according to theinvention.

FIG. 2 is a perspective view of an exemplary apparatus including anocular lens, digital video camera, and a head and chin rest, accordingto the invention.

FIG. 3 is flow chart of an exemplary method for assessing retinal andchoroidal blood flow in a subject, according to the invention.

FIG. 4 is a flowchart of further steps of the exemplary method of FIG.3.

FIG. 5 is a pipeline diagram of an exemplary method according to theinvention.

FIG. 6 is an alternate schematic diagram of an exemplary systemaccording to the invention.

FIG. 7 includes a set of input video frames and a set of enhanced videoframes following enhancement of the input video frames by the systemsand methods of the invention.

FIG. 8 is a graph of signal intensity versus time of a region ofinterest that has been enhanced by the systems and methods of theinvention.

FIG. 9 is a schematic illustration of a region of interest withenhancement showing tissue perfusion over time, along with a graphillustrating quantification of signal intensity versus time afterenhancement by the systems and methods of the invention.

DETAIL DESCRIPTION OF EXEMPLARY EMBODIMENTS

The details of one or more embodiments of the presently-disclosedinvention are set forth in this document. Modifications to embodimentsdescribed herein, and other embodiments, will be evident to those ofordinary skill in the art after a study of the information providedherein. The information provided herein, and particularly the specificdetails of the described exemplary embodiments, is provided primarilyfor clearness of understanding and no unnecessary limitations are to beunderstood therefrom. In case of conflict, the specification of thisdocument, including definitions, will control.

While the terms used herein are believed to be well understood by one ofordinary skill in the art, definitions are set forth herein tofacilitate explanation of the presently-disclosed subject matter.

Unless defined otherwise, all technical and scientific terms used hereinhave the same meaning as commonly understood by one of ordinary skill inthe art to which the presently-disclosed subject matter belongs.Although any methods, devices, and materials similar or equivalent tothose described herein can be used in the practice or testing of thepresently-disclosed subject matter, representative methods, devices, andmaterials are now described.

Following long-standing patent law convention, the terms “a”, “an”, and“the” refer to “one or more” when used in this application, includingthe claims.

The terms “computer,” “computing machine,” “processing device,” and“processor” are used herein to describe one or more microprocessors,microcontrollers, central processing units, Digital Signal Processors(DSPs), Field-Programmable Gate Arrays (FPGAs), Application-SpecificIntegrated Circuits (ASICs), or the like, along with peripheral devicessuch as data storage device(s), input/output devices, or the like, forexecuting software instructions to perform substantial computationsincluding numerous arithmetic operations or logic operations withouthuman intervention during a run.

The term “data storage device” is understood to mean physical devices(computer readable media) used to store programs (sequences ofinstructions) or data (e.g. program state information) on anon-transient basis for use in a computer or other digital electronicdevice, including primary memory used for the information in physicalsystems which are fast (i.e. RAM), and secondary memory, which arephysical devices for program and data storage which are slow to accessbut offer higher memory capacity. Traditional secondary memory includestape, magnetic disks, and optical discs (CD-ROM and DVD-ROM). The term“memory” is often (but not always) associated with addressablesemiconductor memory, i.e. integrated circuits consisting ofsilicon-based transistors, used for example as primary memory but alsoother purposes in computers and other digital electronic devices.Semiconductor memory includes both volatile and non-volatile memory.Examples of non-volatile memory include flash memory (sometimes used assecondary, sometimes primary computer memory) and ROM/PROM/EPROM/EEPROMmemory. Examples of volatile memory include dynamic RAM memory, DRAM,and static RAM memory, SRAM.

Eulerian Video Magnification (EVM), a technique developed at theMassachusetts Institute of Technology, amplifies small changes fromseemingly static video, revealing subtle variations that would beotherwise invisible to the naked eye. This invention modifies andenhances EVM to further advance this technique specifically for retinalimaging. To do this, the invention involves the addition ofpre-processing image stabilization to the EVM algorithm using referencepoints specific to the retina, as well as interfacing with otherbiosensors to continuously refine variables in the algorithm to improvesensitivity and quality. Advantageously, this invention provides anelegant, noninvasive, and inexpensive solution to assess retinal andchoroidal blood flow.

As used herein, the term “perfusion” means the passage of fluid throughthe circulatory system or lymphatic system to an organ or a tissue,referring to the delivery of blood to a capillary bed in tissue.Perfusion is measured as the rate at which blood is delivered to tissue,or volume of blood per unit time (blood flow) per unit tissue mass.

As shown in FIG. 1, an exemplary system 100 according to the inventionincludes an ocular lens 102, a light source 104, a digital video camera106, a biosensor 108, a trigger 110, a computer 112, and a display 114.

The ocular lens 102 is configured for viewing a fundus of an eye 120 ofa subject 122. The subject 122 is preferably a human being, but theexemplary system would also function on eyes of other living animalshaving a measurable pulse. In the exemplary embodiment, the ocular lens102 is a fundus lens, such as a Topcon TRC-50X by Topcon MedicalSystems, Oxland, N.J. (see: FIG. 2). Lenses providing different views ofthe fundus of the eye 120 (e.g., 20, 35, and 50 degree views) can beutilized. Further lenses can be used to give a zoomed view, or a moreperipheral view. Additionally, adaptive optics can be used to accountfor distortions in focus caused by eye movements.

The light source 104 is for illuminating the fundus of the eye 120 ofthe subject 122. The light source 104 is preferably a coherent lightsource producing coherent illumination. However, the light source 104may also be a laser, an incoherent light source, a light sourceproducing differing intensities of light, or a light source producingdifferent wavelengths of light. For example, a near-infrared (NIR) lightsource producing NIR wavelengths of light cause an autofluorescence ofthe retinal pigment epithelium (RPE), which allows visualized thinningof the RPE layer based on increased visualization of vasculature andblood flow, as discussed below. Furthermore, the light source 104 maystrobe or pulse the illumination to reduce eye strain or to enable theuse of higher intensity illumination.

The digital video camera 106 is interfaced to the ocular lens 102 (i.e.,is in optical communication with the lens) (see: FIG. 2) for imaging thefundus of the eye 120 of the subject 122. The digital video camera 106is preferably a consumer-grade digital video camera with a CMOS sensor,such as a Sony A7SII, by Sony Corporation of Tokyo, Japan. However, thedigital video camera 106 may also be a more specialized camera havingimproved spatial resolution (over that of a consumer-grade camera), ormay include other sensor types, such as CCD, or other wavelengthsensitivities, such as NIR, green, blue, etc., or operate at highertemporal frequencies (e.g., 200, 500, 960 frames per second) to captureperfusion and blood flow in subjects having a higher heart rate/pulse.

The biosensor 108 is for sensing a pulse waveform of a body part havinga pulse indication 124 of the subject 122. For instance, the biosensor108 in one embodiment is a pulse oximeter that records oxygen saturationin a subject's finger via photoplethysmography. providing a proxy forpulse. In another embodiment, the biosensor 108 is an electrocardiogram(EKG). In yet other embodiments, the biosensor 108 is a wearable devicefor photoplethysmography, a doppler ultrasound device, an echocardiogramdevice, and even, in an operating room environment, a catheter sensing apulse/pressure waveform in a central line.

The trigger 110 in one embodiment is a hardware trigger including ajoystick with a top button (see: FIG. 2). In other embodiments, thetrigger is a software trigger, or an input from a keyboard, a capacitiveor a resistive touch sensitive button, a touch screen, a game consolecontroller, or a voice activated device.

The computer 112 in in communication with the digital video camera 106,the biosensor 108, and the trigger 110. In some embodiments, thecomputer 112 is a general purpose computer with a processor and a datastorage device/memory. In other embodiments, the computer 112 is a FPGAdedicated to performing the functions discussed below. The computer 112is configured for recording input frames received from the digital videocamera 106 and pulse waveform data from the biosensor 108 in response toan input from the trigger 110. The computer 112 receives the inputframes and the pulse waveform data simultaneously, once recording isinitiated with the trigger 110. On each sample by the digital videocamera 106, the biosensor 108 also senses the pulse waveform of thesubject, providing a proxy for the pulse of the subject 122. Thecomputer 112 syncs the input frames and the pulse waveform data based onthe trigger 110 to record both the input frames and the pulse waveform.

The computer 112 is also configured for defining a low-pass frequencyand a high-pass frequency by a lowest time and a highest time betweenheart beats in the pulse waveform data, stabilizing each of the inputframes utilizing subpixel phase correlation with a reference frame, andenhancing contrast of each of the input frames utilizing contrastlimited adaptive histogram equalization (CLAHE). Once a number of inputframes have been recorded to obtain pulse variability (low pass and highpass frequency), the computer 112 begins stabilizing each of the inputframes on a frame by frame basis utilizing subpixel registration basedon phase correlation of the start frame. Then, the input frames undergocontrast enhancement the CLAHE method, in real time before obtaining thenext frame. Advantageously, the integration of the biosensor allowsnarrowing of the frequency range of interest and boosting thesignal-to-noise ratio of the resulting enhanced frames described below.

The computer 112 is further configured for separating each of the inputframes into sub-channels (e.g., red, green, blue), and conducting oneach sub-channel eulerian video magnification (EVM) for coloramplification using the inputs of image sampling rate, the low-passfrequency, the high-pass frequency, and an amplification factor. In oneembodiment, the amplification factor is a scalar. In another embodiment,the amplification factor is function-based. For example, in oneembodiment, the pulse waveform sensed by the biosensor 108 is normalizedand the normalized waveform is used as an amplification factor function,such that the amplification factor is maximized when the subject's bloodflow/pressure is at a maximum and minimized when the subject's bloodflow/pressure is at a minimum in the pulse waveform. Advantageously, theamplification factor makes perfusion visual without introducing signalartifacts.

Then, the computer 112 is for reconstructing the amplified sub-channelsinto output frames; and combining the output frames with the inputframes, resulting in enhanced frames demonstrating retinal and choroidalblood flow and tissue perfusion. Then, the enhanced frames are eithersaved sequentially to a video file or viewed live on the display 114.

Thus, the invention continuously modifies the input variables toconducting Eulerian Video Magnification with feedback from the user andthe outputs, along with pre-processing and post-processing in order toimprove the quality of the output. In addition, the biosensor 108provides another input variable.

The display 114 is for displaying the enhanced frames. In oneembodiment, the display 114 is a general purpose computer display. Inother embodiments, the display 114 is a virtual reality (VR)head-mounted display, an organic light-emitting diode (OLED) display, ora liquid crystal display (LCD). The computer 112 is further configuredfor adjusting the enhanced frames for brightness, contrast, zoom,rotation, and time, and outputting the enhanced frames to the display114 to visualize retinal and choroidal blood flow and tissue perfusion.

The integration of the ocular lens 102, light source 104, and digitalvideo camera 106 with the biosensor 108 and eulerian video magnification(EVM) is new from the prior art of other retina camera systems and ofprior work accomplished with EVM. Signal cross-correlation of the inputframes (i.e., image sampling) with the pulse waveform data (i.e.,biosensor data) allows for timing the start and end of each pulse, whichis used in conducting EVM. This system allows for visualization ofmicrovasculature dynamics, which has not been done with other prior artthat has utilized EVM.

The prior art, such as other applications of eulerian videomagnification, standard retinal fundoscopy, and static images obtainedthrough indocyanine green angiography, do not include the ability tovisualize blood flow in areas specific to the retina. The tissueanalyzed in prior art was performed on easily accessible tissue withlarge volumes of blood flow i.e. the hand. By integrating the ocularlens 102, the light source 104, the digital video camera 106, thebiosensor 108, and the computer 112 (i.e., processing system), theexemplary system 100 is capable of blood flow visualization at a smallerscale with greater accuracy, allowing for a true readout specific toeach individual in a minimally accessible tissue layer. Note that thisis noninvasive, in that it does not utilize an intravenous contrast dye.The prior art also utilizes a rough estimate of heart rate to select astatic low-pass and high-pass frequency for the eulerian videomagnification step, which leads to artifacts and decreases signal tonoise ratio. The exemplary system 100 records the heart rate with thebiosensor 108 to more accurately enhance changes that correspond withtissue perfusion.

Additionally, the exemplary system 100 also includes a head and chinrest 126 for the subject to rest comfortably without strain. FIG. 2shows an exemplary apparatus including an ocular lens 102, a digitalvideo camera 106, and a head and chin rest 126.

Returning now to FIG. 1, the exemplary system 100 also includes afixation illuminator 128. The fixation illuminator 128 is to reduceocular movements.

In one embodiment, the computer 112 is further configured forquantifying image intensity for a user-selected region of interest (ROI)and generating a heat map of the ROI where intensity changes aregreatest.

FIG. 3 is a flow chart of an exemplary method 200 for assessing retinaland choroidal blood flow in a subject. The exemplary method 200 includesthe steps of: S202 illuminating a fundus of an eye of the subject with alight source; S204 recording, by a computer in response to an input froma trigger, input frames received from a digital video camera and anocular lens configured for imaging a fundus of an eye of the subject;and S206 recording, by the computer in response to the input from thetrigger, pulse waveform data of the subject received from a biosensor.

Step S208 of the exemplary method 200 is waiting until enough pulsewaveform data has been recorded to define a low-pass frequency and ahigh-pass frequency, and step S210 is defining the low-pass frequencyand the high-pass frequency by a lowest time and a highest time betweenheart beats in the pulse waveform data. Then, step S212 is stabilizingeach of the input frames utilizing subpixel phase correlation with areference frame, and step S214 is enhancing contrast of each of theinput frames utilizing contrast limited adaptive histogram equalization(CLAHE).

Next, step S216 is separating each of the input frames intosub-channels, and step S218 is conducting on each sub-channel eulerianvideo magnification (EVM) for color amplification using the inputs ofimage sampling rate, the low-pass frequency, the high-pass frequency,and an amplification factor. In one embodiment, the amplification factoris a scalar. In another embodiment, the amplification factor isfunction-based.

Step S220 is reconstructing the amplified sub-channels into outputframes, and step S222 is combining the output frames with the inputframes, resulting in enhanced frames demonstrating retinal and choroidalblood flow and tissue perfusion. In one embodiment, step S224 is savingthe enhanced frames sequentially to a video file. In another embodiment,step S226 is displaying the enhanced frames live on a display.

The exemplary method 200 further includes step S228 illuminating the eyeof the subject with a fixation illuminator to reduce ocular movements.

FIG. 4 is a flowchart of further steps of the exemplary method 200wherein the pulse waveform data is a pulse oximeter signal, which has atime delay from the perfusion in the input frames. Thus, the exemplarymethod 200 further comprises the steps of: S230 performing temporal fastfourier transform of the input frames; S232 performing temporal fastfourier transform of the pulse oximeter signal; S234 determining amatrix product by matrix multiplication of the temporal fast fouriertransform of the image frames with a complex conjugate of the temporalfast fourier transform of the pulse oximeter signal; S236 performinginverse fast fourier transform of the matrix product; S238 determining apeak of the inverse fast fourier transform of the matrix product toobtain a time delay between the pulse oximeter signal land the imageframes; and S240 shifting the pulse oximeter signal by the time delay.

FIG. 5 is a pipeline diagram of an exemplary method 300 according to theinvention. As shown, the EVM process includes Pyramid Construction(Downsampling), Spatial Filtering, Pulse Selection 302, Enhancements306, and Image Reconstruction (Upsampling). However, unique to thepresent invention, pulse selection 302 involves input from the biosensor(pulse oximeter) 304, which cross-correlates pulse oximeter signal lagwith timing of the input frames, as described above. Enhancements 306involve amplification of temporally filtered signals with a scalar orfunction-based multiplication factor (α_(N)) large enough to makeperfusion visual without introducing signal artifacts. The imagepyramids for each frame are then reconstructed and combined with theinput frames, resulting in enhanced frames demonstrating tissueperfusion.

FIG. 6 is an alternate view of an exemplary system 400 according to theinvention, including an ocular lens 102, a digital video camera 106, abiosensor 108, a computer 112, and a fundus of an eye 120, as describedabove.

FIG. 7 is a set of video frames showing four frames “(a) Input” from anoriginal video sequence showing no change in signal intensity within thedotted area over a two-second period, and the same four frames “(b)Enhanced” following enhancement by the systems and methods describedabove.

FIG. 8 is a graph of signal intensity versus time of a region ofinterest that has been enhanced by the systems and methods of theinvention.

FIG. 9 is a schematic illustration of a region of interest withenhancement showing tissue perfusion over time, along with a graphillustrating quantification of signal intensity versus time after theenhancement of the invention.

As mentioned above, the current standard, ICG angiography, requiresinjection of a dye that is associated with allergic reactions and takesup to an hour to complete acquiring images. Additionally, ICG injectionsare not recommended for certain patients with pre-existing conditionsdue to health complications. Advantageously, this invention can be usedin areas where the equipment and dye are not available and for patientsunable to undergo ICG injection. In some embodiments, invention also hascapabilities of real-time image processing, advantageously creating anefficient diagnostic technique for physicians. In some embodiments, theinvention allows for quantification of blood flow parameters to trackhow the vessels of a patient's retina are changing over multiple visitsrapidly and accurately. Also, in some embodiments, the invention allowsphysicians to set specific regions of interest in the retina forindividual patients, and track the evolution of blood flow in thesedesignated regions over multiple patient visits. This capability trulyallows the physician to better understand and study the development ofdiabetic retinopathy, and potentially other retinal manifestations, asit relates to choroidal-retinal blood flow.

Furthermore, in some embodiments, the invention can be used in thesurgical setting, whereby surgeons can, advantageously, visualize thechoroidal blood flow in real time prior to laser surgical procedures.While one embodiment of the invention focuses on color amplification forassessing blood flow, in other embodiments of the invention amplifiessmall motions.

In some embodiments, the processor unit specifically determines bloodflow parameters for a region of interest in response to receiving aselection of the region of interest input by the operator via an inputdevice. The processor unit, in turn, saves this region of interest forfuture patient visits, in order to track changes over time.

Thus, the invention performs real-time analysis, improves quality of theoutputs, and allows for quantification of blood flow parameters. Theregion of interest magnification, in particular, allows the clinician tobe more specific in the clinician's assessment of the retina of thesubject and to monitor the health of the subject over an extended periodof time.

Advantageously, the invention described hereinabove providesnoninvasive, inexpensive, quick, and accurate visualizations of apatient's retinal blood flow to clinicians and surgeons. Additionally,the invention creates a clinical measurement for blood flow in theretina and choroid that can be tracked over time.

It will be understood that various details of the presently disclosedsubject matter can be changed without departing from the scope of thesubject matter disclosed herein. Furthermore, the foregoing descriptionis for the purpose of illustration only, and not for the purpose oflimitation.

What is claimed is:
 1. A system for assessing retinal and choroidalblood flow in a subject, comprising: an ocular lens for viewing a fundusof an eye of the subject; a light source for illuminating the fundus ofthe eye of the subject; a digital video camera in optical communicationwith the ocular lens for imaging the fundus of the eye of the subject; abiosensor for sensing a pulse waveform of the subject; a trigger; acomputer in communication with the digital video camera, the biosensor,and the trigger, the computer configured for: recording input framesreceived from the digital video camera and pulse waveform data from thebiosensor in response to an input from the trigger; defining a low-passfrequency and a high-pass frequency by a lowest time and a highest timebetween heart beats in the pulse waveform data; stabilizing each of theinput frames utilizing subpixel phase correlation with a referenceframe; enhancing contrast of each of the input frames utilizing contrastlimited adaptive histogram equalization (CLAHE); separating each of theinput frames into sub-channels; conducting on each sub-channel eulerianvideo magnification for color amplification using the inputs of imagesampling rate, the low-pass frequency, the high-pass frequency, and anamplification factor; reconstructing the amplified sub-channels intooutput frames; and combining the output frames with the input frames,resulting in enhanced frames demonstrating retinal and choroidal bloodflow and tissue perfusion; and a display for displaying the enhancedframes.
 2. The system of claim 1, further comprising a head and chinrest for the subject to rest comfortably without strain.
 3. The systemof claim 1, further comprising a fixation illuminator attached to theocular lens to reduce ocular movements.
 4. The system of claim 1,wherein the biosensor is a pulse oximeter.
 5. The system of claim 1,wherein the computer is further configured for adjusting the enhancedframes for brightness, contrast, zoom, or rotation.
 6. The system ofclaim 1, wherein the computer is further configured for quantifyingimage intensity for a user-selected region of interest (ROI) andgenerating a heat map of the ROI where intensity changes are greatest.7. The system of claim 1, wherein the amplification factor is a scalar.8. The system of claim 1, wherein the amplification factor isfunction-based.
 9. A method for assessing retinal and choroidal bloodflow in a subject, comprising: recording, by a computer in response toan input from a trigger, input frames received from a digital videocamera and an ocular lens configured for imaging a fundus of an eye ofthe subject; recording, by the computer in response to the input fromthe trigger, pulse waveform data of the subject received from abiosensor; defining a low-pass frequency and a high-pass frequency by alowest time and a highest time between heart beats in the pulse waveformdata; stabilizing each of the input frames utilizing subpixel phasecorrelation with a reference frame; enhancing contrast of each of theinput frames utilizing contrast limited adaptive histogram equalization(CLAHE); separating each of the input frames into sub-channels;conducting, on each sub-channel, eulerian video magnification for coloramplification using the inputs of image sampling rate, the low-passfrequency, the high-pass frequency, and an amplification factor;reconstructing the amplified sub-channels into output frames; andcombining the output frames with the input frames, resulting in enhancedframes demonstrating tissue perfusion.
 10. The method of claim 9,further comprising illuminating the eye of the subject with a fixationilluminator to reduce ocular movements.
 11. The method of claim 9,further comprising saving the enhanced frames sequentially to a videofile.
 12. The method of claim 9, further comprising displaying theenhanced frames live on a display.
 13. The method of claim 9, furthercomprising waiting to until enough pulse waveform data has been recordedto define the low-pass frequency and the high-pass frequency beforestabilizing each and enhancing the contrast of each of the input frames.14. The method of claim 9, wherein the pulse waveform data is a pulseoximeter signal, and the method further comprising cross-correlating thepulse oximeter signal with the input frames, including: performingtemporal fast fourier transform of the input frames; performing temporalfast fourier transform of the pulse oximeter signal; determining amatrix product by matrix multiplication of the temporal fast fouriertransform of the image frames with a complex conjugate of the temporalfast fourier transform of the pulse oximeter signal; performing inversefast fourier transform of the matrix product; determining a peak of theinverse fast fourier transform of the matrix product to obtain a timedelay between the pulse oximeter signal land the image frames; andshifting the pulse oximeter signal by the time delay.
 15. The method ofclaim 9, wherein the amplification factor is a scalar.
 16. The method ofclaim 9, wherein the amplification factor is function-based.